Tuesday, June 09, 2015

Recently, there has been considerable interest in a paper showing that rainfall in the Sahel has increased likely due to sea surface temperature trends in the North Atlantic as compared to the oceans in general. Now Eli is not here to tell you about that paper by Alessandra Giannini, she has done it herself,

The authors show that while the carbon sink is dominated by forests, especially tropical forests, the annual variability (hi Victor) in the carbon sinks is dominated by arid lands such as the Sahel which makes sense, because in wet years, the semi-arid lands will bloom, in dry ones, not much.
The figure to the right requires some explanation. The y axes are percent contribution to the biosphere's net carbon flux from each of the land types listed at the bottom. It is the difference between the global primary production and the respiration. LPJ-GUESS is a biogeochemical vegetation model and TRENDY is a model intercomparison project, go read the paper for details. IAV is the interannual variation.

Semi-arid lands like the Sahel dominate both the trend and the interannual variation, which makes sense, they are on the margin and small differences in weather make a large difference in the amount of vegetation.

The paper points out that in 2011 there was a large increase in the carbon sink, which is attributed to a very wet year in Australia.

As to the future, a large increase in the carbon sink appears when it is cool and wet in the semi-arid regions, a large decrease when it is hot and dry. In general the level of precipitation is more important than the temperature.

Taking this into account bunnies should go back and look at Giannini's video. If the Sahel is wetter, then there will be more primary production of vegetation, but if it is hotter, there will be more respiration and decay. That means more food, a very good thing, but not as much natural carbon sequestration as if it were cooler

In North Africa, herds are wealth, and the Sahel is massively over grazed - by cattle in the south and sheep in the north.

A group at MIT did a paper on the issue back in the 1970s - they fenced off (and guarded) areas and in a couple of years the fenced off areas returned to grassland while the surrounding areas remained desert.

Overgrazing is a weapon of mass destruction on par with the plow. It was an amplifying factor in the agricultural collapse of Syria. Other examples: Iceland/ Viking Greenland, Chinese Loess Plateau. And then there's virtual overgrazing, like growing soya in deforested Amazon to feed cattle in Texas...

Alan Savory's notions that intensive trampling and grazing can save grasslands are not supported by peer reviewed studies. To put it politely, his views are those of an outlier.

Wiki:"A 2014 review in the International Journal of Biodiversity criticized Savory's methods and assertions, finding little peer-review support for many of his more contentious assertions. The authors concluded that: 'Ecologically, the application of HM [holistic management] principles of trampling and intensive foraging are as detrimental to plants, soils, water storage, and plant productivity as are conventional grazing systems. Contrary to claims made that HM will reverse climate change, the scientific evidence is that global greenhouse gas emissions are vastly larger than the capacity of worldwide grasslands and deserts to store the carbon emitted each year.' "

What happens in the Sahel stays in the Sahel, but the point is that even if rainfall increases the net carbon sequestration will not be large if temperature rises. If the damn goats eat the grass even less.

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Eli Rabett

Eli Rabett, a not quite failed professorial techno-bunny who finally handed in the keys and retired from his wanna be research university. The students continue to be naive but great people and the administrators continue to vary day-to-day between homicidal and delusional without Eli's help. Eli notices from recent political developments that this behavior is not limited to administrators. His colleagues retain their curious inability to see the holes that they dig for themselves. Prof. Rabett is thankful that they, or at least some of them occasionally heeded his pointing out the implications of the various enthusiasms that rattle around the department and school. Ms. Rabett is thankful that Prof. Rabett occasionally heeds her pointing out that he is nuts.